The present invention is generally directed to processes for the preparation of encapsulated toner compositions, and more specifically the present invention is directed to processes for the formulation of encapsulated toner compositions with certain oligomeric surfactants by interfacial polymerization of shell-forming monomers in the presence of a free-radical initiator or initiator and monomer(s) and pigment particles contained in the core, and subsequent free-radical polymerization of the core monomers. Thus, in one embodiment the present invention is directed to a process for the economical preparation of heat fixable toner compositions by interfacial/free-radical polymerization methods wherein there is selected polyethylene oxide, or polyoxyethylene based surfactants. Other embodiments of the present invention relate to interfacial/freeradical polymerization processes for obtaining colored toner compositions. Additionally, the selection of monomer components for the process of the present invention enables a lower cost of production for the desired toner compositions, greater flexibility in the selection of core material properties, and a higher degree of core and toner physical property, for example size diameter control, than can be achieved with the polymers and solvents of the prior art. Also, with the toner compositions of the present invention wherein polyethylene oxide based surfactants are selected, there is avoided undesirable coagulation of toner particles; and these particles are substantially insensitive to relative humidities of, for example, from about 20 to about 80 percent. The aforementioned toners prepared in accordance with the process of the present invention are useful for permitting the development of images in electrophotographic imaging systems, inclusive of electrostatic imaging processes wherein pressure or heat fixing, is selected.
Encapsulated and cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of advantages in comparison to toners that are fused by heat, primarily relating to the requirements for less energy since the toner compositions used can be fused at room temperature. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions must usually be fused under high pressure, which has a tendency to severely disrupt the toner fusing characteristics of the toner selected. This can result in images of low resolution, or no images whatsoever. Also, with some of the prior art cold pressure toner compositions substantial image smearing can result from the high pressures used. Additionally, the cold pressure fixing toner compositions of the prior art have other disadvantages in that, for example, these compositions are prepared with solvents that may create explosion hazards; and further these solvents are costly in that separation and recovery equipment is required. Moreover, the selection of the aforementioned solvents may decrease the percentage yield of toner product obtained; and also these solvents limit flexibility requirements in the selection of the core polymer.
With further specific reference to the prior art, there is disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there is disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there is disclosed in the prior art encapsulated toner compositions containing pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Moreover, illustrated in a copending application U.S. Ser. No. 621,307, now U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. Ser. No. 718,676, now abandoned, the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process.
Furthermore, in U.S. Pat. No. 4,727,011, the disclosure of which is totally incorporated herein by reference, there are illustrated processes for encapsulated toner compositions comprised of a core containing pigment particles, and a free-radical polymerized monomer(s) with an optional polymer, such as polyisobutylene, in an amount of from about 1 to about 5 percent by weight, and a shell generated by interfacial polymerization processes. More specifically, the process illustrated in this patent, which is accomplished in the absence of a solvent, is comprised of (1) mixing a blend of a core monomer, or monomers not exceeding five, free-radical chemical initiator, pigment, and a first shell monomer; (2) forming an organic liquid:solid suspension, in a stabilized aqueous suspension; (3) thereafter forming a liquid suspension; and (4) subsequently subjecting the aforementioned mixture to an interfacial polymerization by the addition of a water-soluble second shell monomer. After the polymerization is complete, a free-radical polymerization is initiated by increasing the temperature of the suspension, for example, to 75.degree. C., and thus commencing the disassociation of the chemical initiator to free-radicals capable of polymerizing the core monomer(s). Moreover, for obtaining particles with narrow size distributions, that is toner particles with an average diameter of from about 10 to about 35 microns, and geometric size dispersities of less than 1.20, subsequent to the interfacial polymerization step the toner product can be submitted to a free-radical polymerization permitting the particles to agglomerate and polymerize together through partially formed shells. These partially formed shells can be produced by reducing the degree of homogeneity of the original blend of shell material thus biasing the distribution of shell material in favor of large particles, and promoting interparticle polymerization and growth of smaller particles resulting in a narrowing of the size distribution. As stabilizers, there are disclosed in the '011 patent polymeric water soluble molecules such as polyvinylalcohols, reference for example page 10 thereof. Also, the process of the present invention is directed to the preparation of encapsulated toner compositions which comprises mixing in the absence of solvent core monomer, an initiator, pigment particles, monomer(s), stabilizer and water; thereafter adding a second shell monomer thereby enabling an interfacial polymerization reaction between the first and second shell monomers; and subsequently affecting a free-radical polymerization of the core monomer.
Liquid developer compositions are also known, reference for example U.S. Pat. No. 3,806,354, the disclosure of which is totally incorporated herein by reference. This patent illustrates liquid inks comprised of one or more liquid vehicles, colorants such as pigments and dyes, dispersants, and viscosity control additives. Examples of vehicles disclosed in the aforementioned patent are mineral oils, mineral spirits, and kerosene; while examples of colorants include carbon black, oil red, and oil blue. Dispersants described in this patent include materials such as polyvinyl pyrrolidone. Additionally, there is described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphiphilic block or graft copolymeric stabilizer irreversibly chemically, or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
Free-radical polymerization is also well known in the art, and can be generalized as bulk, solution, or suspension polymerization. These polymerizations are commonly selected for the preparation of commodity polymers. The kinetics and mechanisms for free-radical polymerization of monomer(s) are also well known. In these processes, the control of polymer properties such as molecular weight and molecular weight dispersity can be affected by initiator, species concentrations, temperatures, and temperature profiles.
Many prior art processes provide deleterious effects on toner particle morphology and bulk density as a result of the removal of solvent, and the subsequent collapse of the toner particles during particle isolation resulting in a toner of very low bulk density, which disadvantages are substantially eliminated with the process of the present invention. More specifically, thus with the process of the present invention control of the toner physical properties of both the core and shell materials is permitted. Additionally, the toner compositions prepared in accordance with the process of the present invention have hard shells thus enabling images of excellent resolution with substantially no background deposits for a number of imaging cycles, and toner aggolmeratrion is avoided. Also, the toner compositions prepared in accordance with the process of the present invention contain as a protective stabilizing colloid a polyethylene oxide surfactant which enables minimum coagulation of the resulting particles, and are insensitive to relative humidity of, for example, from about 20 to about 80 percent.
Accordingly, there is a need for improved processes for the preparation of encapsulated toner compositions. Also, there is a need for interfacial polymerization processes for black and colored encapsulated toner compositions, wherein the core contains a polymerizable monomer and free-radical initiator together with pigments and other materials, and wherein there is selected as surfactants, or protective colloids polyethylene oxide based components. There is also a need for simple, economical processes for the preparation of encapsulated toner compositions in high yields, which processes are affected in the presence of polyethylene oxide, or polyoxyethylene based components. Additionally, there is a need for simple economical polymerization processes that will permit the generation of encapsulated toner compositions, especially compositions with hard, durable shells, excellent toner flowability, and wherein these compositions are insensitive to relative humidities of from about 20 to about 80 percent. Furthermore, there is a need for improved processes that will enable toner compositions with hard shells and soft cores, whose properties such as molecular weight, molecular weight dispersity, and degree of crosslinking can be independently controlled. Moreover, there is a need for processes for the preparation of encapsulated toners wherein coagulation of the toner particles is avoided. Additionally, there is a need for processes for the preparation of encapsulated toners wherein the volume average toner particle size is from about 5 to about 30 microns with GSD of from about 1.3 to about 1.8. In addition, there is a need for process that will enable the fabrication of toner particles with clean surfaces, that is wherein the surfaces are free from surfactants and ultrafine particles with, for example, an average particle diameter of less than 1 micron. Furthermore, there is a need for the rapid economical preparation of toner compositions wherein low molecular weight polyoxyethylene surfactants, which can be removed easily by washing with water, are selected. Moreover, there is a need for increasing the concentration by, for example, an amount of from about 5 to about 15 weight percent of pigment particles within the toner compositions illustrated herein by selecting polyethylene oxide based components as surfactants, and protective colloids.